Question 1
a) Write the chemical formula and the molar mass (g/mol) for the amino acid selenocysteine.
b) Complete the table by writing the relative masses (g) and %'s of the elements found in 1 mole of selenocysteine.
|
Element
|
Mass (in g) of element in 1 mole of selenocysteine
|
% of element in 1 mole of selenocysteine
|
|
C
|
|
|
|
H
|
|
|
|
N
|
|
|
|
O
|
|
|
|
Se
|
|
|
c) Stachyose is a tetrasaccharide found in vegetables and many plants. You are provided with a 0.8 M solution of stachyose.
Molar mass: stachyose (C24H42O21) = 666.58 g/mol.
What volume (in mL) will contain 350 μmoles of stachyose?
Question 2
a) Calculate the concentration of hydrogen ions [H+] for
- Lemon juice, pH 2.1
- Icelandic Glacial brand water, pH 8.4
- Milk, pH 6.5
b) Calculate the pH of
- 85 mM NaOH
- Milk of Magnesia, [H+] = 3.20 x 10-11 M
- 2.2 M Hydrobromic acid (HBr)
c) Calculate the pH obtained by dissolving 3.68 g of anhydrous
potassium ethanoate (MW = 98.14 g/mol) in 100 mL of 0.25 M ethanoic acid, given that the pKa of ethanoic acid = 4.75.
Question 3
You need to prepare 100 mL of a 0.5 M solution of LiCl.
You have 50 mL of a 0.65 M LiCl solution and 20 mL of a 5% (w/v) LiCl solution.
- Molar mass of LiCl = 42.39 g/mol
- % (weight / volume) means mass (in g) in volume (100 mL)
What volume of 5% LiCl and water needs to be added to the 50 mL of 0.65 M LiCl solution to make up 100 mL of 0.5 M LiCl?
Show your working for solving this question and complete the table below.
Question 4
Midori Melon Liqueur contains 20 % (v/v) ethanol, Wolf Blass Platinum Label Shiraz contains 14 % (v/v) ethanol and Old Speckled Hen Ale contains 5 % (v/v) ethanol.
- Absolute (100% vol/vol) ethanol: density = 0.79 g/mL
o %'s are vol/vol → i.e., volume of EtOH in 100 mL total volume
- Molecular weight of ethanol = 46.1 g/mol
a) Calculate the molarity of absolute ethanol (100% vol/vol).
b) Calculate the concentration of ethanol in the 3 separate beverages.
- Give the concentrations in g/L
- Give the concentrations as molarities
c) Determine the mass (g) of ethanol in each of the following 3 beverages.
- 500 mL bottle of Midori Melon Liqueur
- 750 mL bottle of Wolf Blass Platinum Label Shiraz
- 6 pack (6 x 355 mL bottles) of Old Speckled Hen Ale
Which beverage contains the highest amount (in g) of ethanol?